1. Technical Field
The present disclosure regards an encapsulated micro-electro-mechanical device, in particular a MEMS acoustic transducer, such as a microphone.
2. Description of the Related Art
As is known, microphones built in MEMS (micro-electro-mechanical system) technology generally comprise a first chip integrating a pressure sensor and a second chip integrating an electronic circuit for processing electrical signals (read circuit). The two chips may be mounted on a support and encapsulated in a package that mechanically protects the chips, above all the microphone, which is in itself fragile and very subject to damage. Furthermore, the package may have metal structures forming Faraday cages for eliminating electromagnetic interference.
Various types of package forming Faraday cages are known for integrated circuits. For example, in some solutions, the package is formed by a base, on which a support for the chips is bonded, and by a cap soldered to the base. For example, the cap may have a metal coating, and the base may be made of metal, being for instance formed by the lead frame for electrically connecting chips (e.g., see “MEMS Packaging”, Bruce K. Gale et al., Oct. 11, 2001, http://www.mech.utah.edu/˜gale/mems/Lecture%2016b%20MEMS%20 Packaging.pdf; and “Si-based Microphone Testing Methodology and Noise reduction”, C. S. Premachandran et al., Symposium on Design, Test, Integration, and Packaging of MEMS/MOEMS, Proceedings of SPIE Vol. 4019 (2000))•0277-786X/OOI). Alternatively, the base may comprise metal layers, for example alternating with insulating materials (see, for example, US 2007/071268; U.S. Pat. No. 6,781,231; U.S. Pat. No. 7,166,910; EP 1 755 360; U.S. Pat. No. 7,434,305; US 2004/046 245; U.S. Pat. No. 7,436,054; U.S. Pat. No. 7,381,589; and WO2007/054070).
However, known solutions are either complex or costly, and thus leave room for improvement. In particular, in certain solutions it is problematical to apply the metal coating via usual sputtering operations on account of the depth of the structures in the cap. Furthermore, in all cases, the process is costly and far from suited to devices, such as microphones, that are to be used in cell phones and the like, the costs of which should be as low as possible.